Passive Injection of a Chemical Solution into a Process Stream

ABSTRACT

A system and method of injecting a chemical into a high pressure process stream without pumps or other active components. The system utilizes the differential pressure created by resistive losses of downstream components within a high pressure process stream. A bypass side stream is taken from an upstream pressure location and returned to the downstream side of the resistive inline process component. The chemical solution vessel is pressurized by the higher side of the pressure differential. The solution then passes through a flow controlling capillary tube exiting on the lower pressure differential side into the bypass stream. The high flow rate chemically diluted bypass stream then returns to the process stream at the lower differential process stream tie-in. The chemical solution is isolated from the process water pressuring the vessel by a movable separating device preventing mixing of the two fluids. The vessel can also be pressurized by gas.

TECHNICAL FIELD OF THE INVENTION

This invention relates to a method and process for injecting a chemical solution into a flowing, pressurized fluid stream.

BACKGROUND

In various industries such as the power generation industry, there is a need to inject chemical solutions into flowing process streams at elevated pressures and temperatures for various purposes. In particular, it is necessary to inject solutions of noble metal containing chemicals, such as Na₂Pt(OH)₆, into the feedwater piping of boiling water nuclear reactors to aid in inhibiting intergranular stress corrosion cracking of susceptible structural materials in the reactor vessel in the presence of hydrogen.

As reported by Hettiarachchi and Diaz, the noble metal chemical solution Na₂Pt(OH)₆ is added to the feedwater piping of boiling water nuclear reactors over a 10 day period. Such 10 day injection periods are repeated during each subsequent yearly fuel cycle. For boiling water nuclear reactors with longer fuel cycles, the 10 day applications are conducted on an annual basis. The total mass of noble metal injected annually is also limited to a fixed value by an industry consensus standard described by Garcia et al. Because of a phenomenon known as “crack flanking”, described by Andresen and Kim, it is advantageous to inject the noble metal chemical over the entire operating period of a fuel cycle, not just during an annual 10 day period. Active metering pumps used for these 10 day injections, such as positive displacement pumps, have experienced maintenance problems due to interaction with the noble metal chemicals such as Na₂Pt(OH)₆ and are not optimum for long term injection.

A boiling water nuclear reactor that follows the industry consensus recommendation will typically add between 200 and 1, 200 gm of Pt (as Na₂Pt(OH)₆) each calendar year, depending on plant specific features such as fuel surface area and power rating. If the addition is made continuously at a constant rate over 365 days, the addition rate will vary between 3.8×10⁴ and 2.3×10⁻³ gm (Pt)/min. If the feedstock is a 1% solution of Na₂Pt(OH)₆, the addition rate will be between 0.038 and 0.23 ml/minute (cc/m). The resulting concentration of Pt in the feedwater would be on the order of 10 parts per trillion. Accordingly, there has been a need in the nuclear industry for a chemical injection system that does not employ active pumps and is capable of adding small, metered amounts of noble metal chemicals, such as Na₂Pt(OH)₆, into the feedwater during the entire fuel cycle.

U.S. Pat. No. 8,054,933 (Tran et al) describes a method of injecting chemicals into flowing nuclear reactor water streams teaching the use of positive displacement pumps, a process computer, various valves, chemical storage tanks, weighing scales and a source of deionized water. While this system is useful in injecting chemicals over short periods of time, it is quite complicated and not necessarily suited for trouble free injection of dilute solutions over longer periods of time.

U.S. Pat. No. 2,266,981 (Miller) discloses a method and apparatus for injecting chemicals into a natural gas pipeline operating at elevated pressures that does not use a pump. The apparatus teaches a fluid supply for storing the chemical to be injected, a pressure feed tank for pressurizing and injecting the chemical into the pipeline and a series of lines, manual valves and gauges for controlling the flow of chemicals from the supply tank into the feed tank and ultimately into the pipeline using gravity. The natural gas line pressurizes the pressure feed tank to the same pressure as the gas in the pipeline and gravity allows the solution in the pressurized tank to flow into the gas pipeline. This arrangement would not work in adding low flow rates of chemicals into a flowing water filed pipe; as the pressurizing gas above the liquid in the feed tank would eventually become saturated. Degassing of the feed solution within the flow restrictor (valve, capillary) would occur and alter the rate of injection precision. An active flow rate control is required to maintain a constant injection rate as the change in height of the feed solution drains the tank. U.S. Pat. No. 6,779,548 (McKeary) teaches a similar method as U.S. Pat. No. 2,266,981 (Miller) but adds a system for automatically controlling the quantity of chemical injected into a pressurized gas system by employing two tanks, one pressurized and one not pressurized. While this system could work well adding liquid to a gas process stream, it will not control a liquid addition to a liquid stream to the accuracy and precision required for very low flow rates required in Pt injection nuclear applications. Similar problems will occur as with U.S. Pat. No. 2,266,981 (Miller)

All injection patents researched for this application have some sort of active displacement component, do not account for dilution of the primary injection solution, have cover gas pressurization (that saturate the chemical injection solution), have active flow controls, or cannot yield very low flow rates (sub ccm) continuously over very long periods (months-year) without intervention.

SUMMARY OF THE INVENTION

A reliable method of injecting small, accurate amounts of a chemical solution into a flowing process stream over long periods of time without the use of pumps is desired by some industries. Described herein is such a chemical injection system and method that uses the pressure drop in a process line as the motive force acting on a variable volume reservoir coupled with a passive, calibrated capillary tubing element to accurately control and meter the additions of a chemical into a liquid process stream at a location of lower pressure within the same line. The system is located in the process line where resistive components create pressure losses as the process fluid passes through, such as before and after a heat exchanger. The amount of solution injected by the system is determined by one control valve and a differential pressure meter measuring the fluid pressure differential location immediately before and immediately after the capillary tubing element. A method is also described in which a pressurized gas, rather than the higher pressure location of the process stream, provides the motive force acting on the variable volume reservoir. In both cases, a bypass stream taken from a high pressure portion of the process stream and introduced into a lower pressure location of the process stream is integral to the invention. The overall advantage of the process is to continuously and passively add metered amounts of a chemical solution in amounts as low as or lower than 0.01 milliliters per minute over periods of over 12 to 24 months.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of the first embodiment of a method of passive injection of a chemical solution into a liquid process stream in accordance with the present invention.

FIG. 2 is a schematic representation of the second embodiment of a method of passive injection of a chemical solution into a liquid process stream in accordance with the present invention. It is similar to the method of FIG. 1, but that the bellows separator arrangement between lines 10 and 19 in FIG. 1 is replaced with the piston separator arrangement shown in FIG. 2.

FIG. 3 is a schematic representation of the third embodiment of a method of passive injection of a chemical solution into a liquid process stream in accordance with the present invention. It is similar to the method of FIG. 1, but that the bellows separator arrangement between lines 10 and 19 is replaced with the membrane separator arrangement shown in FIG. 3.

FIG. 4 is a schematic representation of the fourth embodiment of a method of passive injection of a chemical solution into a liquid process stream in accordance with the present invention as shown in FIGS. 1 through 4, but locates the metering capillary at the entrance to the pressure vessel between lines 9 and 10 rather than at the exit of the pressure vessel, between line 19 and valve 22.

FIG. 5 is a schematic representation of the fifth embodiment of a method of passive injection of a chemical solution into a liquid process stream in accordance with the present invention. It is similar to the method in FIGS. 1 through 3, but replaces the liquid pressurization source at location 7 with a gas pressurization source.

FIG. 6 is plot of capillary tubing flow rates versus pressure drop calculated with Poiseuille's Law for internal diameters of 0.005″ and 0.007″ and lengths of 30″ and 60″. The dashed lines within the plot are the results of the calculations using Poiseuille's Law. A calibration measurement was conducted on a 0.005″ by 60″ capillary tube and is shown also on FIG. 6 as the solid plotted line. The correlation between the calculated 0.005″×60″ rate and measured rate at 50 psig indicates that the application of capillary flow control is valid.

FIG. 7 is a schematic representation of an optional exit embodiment of a method of passive injection of a chemical solution into two liquid process streams in accordance with the present invention. The arrangement shown in the FIG. 7 would replace the hardware downstream of the differential conductivity meter 26 in FIGS. 1 through 5 to allow for the injection into two process streams.

FIG. 8 is a schematic representation of an optional exit embodiment of a method of passive injection of a chemical solution into one process streams in accordance with the present invention. The arrangement shown in the FIG. 8 would replace the hardware downstream of the differential conductivity meter 26 in FIGS. 1 through 5 to allow for the injection into one or two process streams. The flow metering orifice 29 and/or 41 is replaced with a flow controlling sized orifice 45 and the differential pressure gauge 30 is replaced with a pressure gauge 46.

FIG. 9 is a schematic representation of the optional eight embodiment of a method of passive injection of a chemical solution into a process stream in accordance with the present invention. Whereas the schematic in FIG. 1 has only one chemical subsystem between location tees 7 and 23, embodiment eight adds a second chemical subsystem attached at location 7 and 23.

DETAILED DESCRIPTION

The system and method according to the present invention will be described in the context of injection of Na₂Pt(OH)₆ into the feedwater of a boiling water nuclear reactor. This is done for purposes of illustration only and is not intended in a limiting sense. The system and method of the present invention are equally suitable for use in other industries in which low flow rates of chemicals must be dispensed with a high level of accuracy without any active components, such as metering pumps.

First Through Fourth Embodiments—Structure

Referring to FIG. 1, a first embodiment of a method for passive injection of a chemical solution into a high pressure process stream system in accordance with the present invention generally includes the basic concepts that follow. The main process stream, to which the chemical is to be injected is represented by the dashed lines located on the right side of FIG. 1, called the feedwater system, is not a part of the embodiment. The injection system is comprised of a bypass stream line 24 and a chemical injection branch 19. The high flow (1 to 10 liters/min) bypass loop starts at the system inlet 1 and consists of a heat exchanger 2 (which is cooled by service water 3), an isolation valve 6, a capillary pressure control valve 25, a bypass flow control vale 28, a bypass flow element 29, a second isolation valve 31 and ends via line 32 which enters a tee junction into the feedwater. There are four monitoring devices in the bypass loop, a temperature indicator 4 and a pressure gauge 5 located immediately downstream of the heat exchanger, a differential conductivity meter 26 (with inputs immediately before and after the tee junction 23 between valves 25 and 28), and a differential pressure meter 30 located with inputs before and after the bypass flow metering orifice 29. The chemical injection branch consists of a line teed off the bypass loop immediately downstream of isolation valve 6 at tee junction 7 followed by an isolation valve 8 feeding a pressurizing fluid stream 9 into a pressure vessel 13 through line 10. The resulting pressurized fluid 14 acts against the bellows separator 15 forcing the chemical solution 16 out of the pressure vessel through line 19 then through a capillary solution flow control segment 20 through an isolation valve 22 into the feedwater bypass loop at the tee junction 23. The valves 17 and 12 are used for solution fill and vent/drain via the solution fill line 18 and the fill vent/drain line 11 respectively. A capillary differential pressure gauge 21 is located with inputs at both ends of the capillary solution control tubing 20. The key design components are: the chemical 16 separation 15 from the pressuring fluid 14 to prevent dilution, a very low chemical flow rate control capillary flow device 20, a high bypass flow rate through line 24 and utilization of the pressure drop as the main process passes through inline components.

First Embodiment—Operation

Embodiment one in FIG. 1 incorporates common features of this injection system seen also in embodiments two through four herein. They are:

-   -   a. the bypass stream 24 developed from a higher pressure process         stream location 1, for example at the process feedwater pump         exit, to a lower pressure process stream location further         downstream 32, such as after a pressure loss through a process         component such as a heat exchanger and flow nozzle. The bypass         water is first conditioned by a heat exchanger 2 with service         water 3 or optional cooling water on the secondary side. Valves         6 and 31 are used to isolate the injection system when         necessary. The flow rate in the bypass stream line 24 is         affected by the restrictions in the bypass stream including the         heat exchanger 2, the isolation valves 6 and 31, the capillary         pressure control valve 25, the bypass flow control valve 28, and         the flow meter orifice 29. The major control restrictions are         the capillary pressure control valve 25 and the bypass stream         control valves 28. The desired flow rate at line 32 is         controlled and monitored with a calibrated flow metering orifice         29 and its associated differential pressure gauge 30.     -   b. the second common feature of these injection systems is the         chemical solution injection subsystem tee junction 7 through tee         junction 23 (which contains the pressure vessel 13 and the         capillary flow restrictor 20) that controls the rate of chemical         injected into the bypass stream. The pressure vessel is         pressurized with the liquid obtained from the bypass stream at         tee junction 7. A separator 15 inside the pressure vessel         prevents the pressurizing fluid 14 from mixing with the chemical         solution 16 located on the other side of the separator. The         separator 15 moves within the pressure vessel 13 such that the         pressure on both sides is the same, that is, both the pressuring         fluid 14 and chemical solution 16 are at the same pressure.         Valve 25 controls the pressure drop across the capillary flow         control device 20 since the pressure at line 19 is the same as         at location line 24 and the capillary exit pressure and valve         exit pressure are the same at tee junction 23. The chemical         solution 16 from the chemical solution subsystem at tee junction         7 through tee junction 23 is diluted as it flows into the bypass         stream at tee junction 23. The transit time of the chemical         solution from tee junction 23 to the feedwater injection tap         through line 32 is minimized by the high bypass flow rate, thus         minimizing the potential of premature Na₂Pt(OH)₆ thermal         degradation and Pt deposition in undesired locations. To provide         the low flow rates required for Na₂Pt(OH)₆ chemical additions to         boiling water nuclear reactor applications, a capillary solution         flow control device 20 made of small diameter capillary tubing         is located at either the exit of pressure vessel 13 in FIG. 1         through FIG. 3, or at the entrance of pressure vessel 13 in         FIG. 4. To verify the proper flow rate is being accomplished, a         differential pressure measurement 21 is made across the         capillary tube 20 and compared to the capillary calibration         behavior for the particular capillary being used. An example of         a capillary verification behavior chart is shown in FIG. 6.         Poiseuille's Law was used to calculate the flow rate of water at         different pressure drops, tubing lengths (30″ and 60″) and         tubing internal diameters (0.005″ and 0.007″). A tube of 0.005″         internal diameter by 60″ long was tested for flow versus         pressure drop. The measured values are plotted (solid line) and         compared to a Poiseuille's Law calculation (dotted line) and         compare very well in FIG. 6. Poiseuille's Law for flow is         proportional to the length and to the fourth power of the         radius. Other capillary diameters and lengths are plotted in         FIG. 6 as dotted lines. This plot indicates the potential flow         rates of chemical solution required over the expected process         stream flow rates (0.03 ccm to 0.25 ccm) are easily accomplished         with capillary tubing. Other flow rates can be accomplished with         smaller or larger capillary internal diameters and lengths.

In addition to the normal chemical injection operation of the system, there are two other procedures necessary: 1) the initial start-up of the system and 2) subsequent refilling of the vessel after an operational period. Both procedures require the chemical injection subsystem be isolated from the bypass stream by closing valves 8 and 22. Both procedures require ambient pressure conditions. The initial start-up will require filling pressuring fluid volume 13 with high purity water via valve 12 and fill line 11 and then the chemical solution volume 16 with the chemical solution to be added utilizing solution fill line 18 and valve 17. Once the two volumes are completely full (no air gaps), the fill 17 and vent isolation 12 valves can be closed.

The refill procedure is simpler since there should be no air pockets after the initial operating period. The liquid pressuring fluid 14 only needs to be vented via valve 12 while the chemical solution is transferred into the upper chamber 16 until the separator 15 is fully extended. Once the chemical solution chamber 16 is full the fill 17 and vent 12 valves should be closed.

After the initial filling or after subsequent refills, the isolation valves 8 and 22 of the injection subsystem can be opened slowly. If the bypass stream is flowing, the chemical solution will start to flow. If the bypass stream is off-line, as soon as the system is placed into service the chemical solution will start to flow.

To place the system into service, start with valves 6, 25, 28 and 29 closed. Start the service water flow 3 to the heat exchanger 2 then fully open the isolation valves 6 and 31. Slowly open the capillary flow control vale 25 and bypass flow control valve 28 while maintaining a vigil of the temperature 4 exiting the inlet heat exchanger. Open both flow control valves 25 and 28 until the desired capillary differential pressure 21 and bypass differential pressure 30 are obtained. Some iteration of the valve positions may be required, since the two control points and flow rates are not independent. Using the desired chemical solution flow rate, the desired capillary differential pressure gauge value is determined from the correct capillary diameter/length line from a plot like that shown in FIG. 6.

After a period of time, the measured differential conductivity 26 should indicate that chemical is being injected. The downstream conductivity value, after tee junction 23, should be higher than the bypass water, after valve 25. The measured difference can be corroborated by knowing the solution chemical ionic properties, the chemical solution injection rate and the bypass flow rate. A monitoring delay time is necessary to allow the temperature and flow transients to dissipate.

Second Embodiment—Structure

Referring to FIG. 2 shows the second embodiment of the invention identical to that in FIG. 1 except that between line 10 and line 19, where the bellows separator is replaced by a floating piston separator 33 using O-ring seals 34. The vessel design would be changed to accommodate the piston seal movement against the vessel walls. The pressurizing fluid 14, the chemical solution 16, the vent/drain line 11, valve 12, solution fill line 18 and fill valve 17 would remain schematically the same.

Second Embodiment—Operation

All of the operation procedures for the second embodiment, shown in FIG. 2, are the same as the operation procedures for the first embodiment. The separation device is a floating piston 33 with one or more O-ring type seals 34. The piston seal cavity and O-ring size would be manufactured to allow for a low friction sliding motion. The vessel 13 walls would be manufactured to accommodate for near zero bypass of the pressurizing fluid 14 mixing with the chemical solution 16. The floating piston 33 accomplishes the same objective as the bellows separator 15 in FIG. 1, separating the pressurizing fluid from the chemical solution. In some situations the use of the floating piston would be advantageous.

Third Embodiment—structure

Referring to FIG. 3 shows the third embodiment of the invention identical to that in FIG. 1 except that between line 10 and line 19 whereas the bellows separator is replaced by a flexible membrane separator 35. The vessel design would be changed to accommodate for sealing the flexible membrane 35 sandwiched between two flanges in the middle of the vessel. The pressurizing fluid 14, the chemical solution 16, the vent /drain valve line 11, valve 12, solution fill line 18 and fill valve 17 remain schematically the same.

Third Embodiment—Operation

All of the operation procedures for the third embodiment, shown in FIG. 3, are the same as the operation procedures for the first embodiment. The separation device is a flexible membrane 35 which is stretchable to accommodate the volume of chemical for one operating period. The flexible membrane accomplishes the same objective as the bellows separator 15 in FIG. 1, separating the pressurizing fluid from the chemical solution. In some situations the use of the flexible membrane would be advantageous.

Fourth Embodiment—Structure

Referring to FIG. 4 shows the fourth embodiment similar to that shown in FIG. 1 except that the capillary solution flow control 20 is located just after 9 and before the pressure vessel 13. The capillary differential pressure gauge 21 has input lines located between isolation valve 8, on line 9, and between the capillary output on line 10 at the entrance of the pressure vessel 13. The pressurizing fluid 14, the pressure vessel 13, the chemical solution 16, the vent/drain line 11, valve 12, solution fill line 18 and fill valve 17 remain schematically the same.

Fourth Embodiment—Operation

All of the operation procedures for the fourth embodiment, shown in FIG. 4, are the same as the operation procedures for the first embodiment. The only difference being the location of the capillary flow control device 20 at the entrance of the pressure vessel. The fourth embodiment utilizes the principals of hydrodynamics and incompressible liquids. Since the pressure vessel 13 is filled with liquids, for both the pressuring fluid 14 and chemical solution 16, the flow rate entering the vessel equals the flow rate out of the vessel. This embodiment can also be utilized in embodiments one, two and three without any procedural changes.

Fifth Embodiment—Structure

Referring to FIG. 5, the fifth embodiment is similar to that in FIG. 1 except that a high pressure gas supply 36, rather than the water from the bypass loop 24, is used to pressurize the pressure vessel 13 in volume 14. The gas pressure is controlled by the pressure regulator 37, which includes a pressure gauge 38. The gas pressurizing fluid enters the pressure vessel 13 through line 10.

Fifth Embodiment—Operation

The fifth embodiment, shown in FIG. 5, changes the source of vessel pressurization to that of a high pressure gas supply instead of the liquid supplied by the bypass stream 24, shown in FIGS. 1 through 3 at junction tee 7. This change also alters the chemical supply subsystem isolation during the initial filling and subsequent refilling procedures. Embodiment five will not work with embodiment four, where the capillary flow control 20 is in line 10 at the vessel 13 entrance.

The initial and subsequent filling of the vessel is accomplished by closing the high pressure gas supply at valve 39 and the chemical injection valve 22. With valve 12 in the open position the chemical solution is added via line 18 through the open valve 17. When sufficient chemical solution has been added to the chemical solution reservoir 16, valve 17 and valve 12 are closed. The pressure regulator 37 is then set to the desired initial gas pressure on gauge 38. Valve 39 is then opened. Valve 22, where the chemical solution is injected into the bypass stream, is then opened. If not already open, valves 1 and 32 are opened. The capillary pressure control valve 25 is set to wide open (in embodiment five there is no initial need to adjust the capillary pressure control valve 25 to obtain the desired chemical solution flow rate). The desired capillary differential pressure gauge value 21 is obtained by adjusting the pressure regulator 37 to obtain the desired differential pressure across the capillary flow device 20. The downstream pressure of the capillary flow control device is the pressure measured at pressure indicator 5. Thus the differential pressure drop across the capillary flow control device 20 is the difference between pressure gauge 38 and pressure gauge 5.The bypass flow control valve 28 is used to set the bypass stream flow rate.

Sixth Embodiment—Structure

Referring to FIG. 7, the sixth embodiment is applicable to embodiments 1 through 5 of this invention, wherein the components after the differential conductivity cell 26 tie into line 27, items 28 through 32 are duplicated with items 40 through 44 as shown in FIG. 7, allowing controlled injection into two feedwater lines.

Sixth Embodiment—Operation

All five of the embodiments in FIGS. 1 through 5 show a single exit variable bypass flow control valve 28, a single bypass flow metering orifice 29, a single differential pressure gauge 30 and a single isolation valve 31 for a single chemical addition point into one process stream pipe through line 32. Embodiment six, shown in FIG. 7, shows a multiple exit approach that can be incorporated into each of the embodiments one through five. Embodiment six only changes the procedures in embodiments one through five because of adjustments associated with two flow control valves 28 and 40 instead of one are required. The operation of the second exit flow path is the same as for the single path approach. The bypass stream flow rate may have to be increased to accomplish similar attributes of lowering the transit times and maintaining high velocities to lower the potential of premature platinum chemical thermal degradation. All other procedures within the embodiments one through five are applicable.

Seventh Embodiment—Structure

Referring to FIG. 8, the seventh embodiment is applicable to embodiments one through five of this invention, wherein the components from the differential conductivity cell 26 tie in to line 27, item 28 is removed, the flow metering orifice 29 is replaced with a flow controlling orifice 45 and the differential pressure gauge 30 is replaced with a pressure gauge 46.

Seventh Embodiment—Operation

Embodiments one through five have a bypass flow control valve 28, a flow meting orifice 29, a differential pressure meter 30 and an isolation valve 31. The seventh embodiment replaces the flow metering orifice 29 (small pressure drop) and flow control valve 28 with a controlling orifice 45, sized to specifically control the desired flow rate for the bypass. The flow regulating valve 28 is removed. The differential pressure gauge 30 is changed to a pressure gauge 46. Whereas the bypass flow rate was controlled by the valve 28, with a flow metering system (orifice 29 and differential pressure measurement 30), embodiment seven incorporates an orifice that is sized for the pressure drop developed across the components in the main process stream between locations 1 and 32 minus the pressure drop across valve 25.

Embodiment six has two exit paths which duplicate the same exit hardware for a second feedwater injection stream, items 40, 41, 42, and 43. In FIG. 7, these parallel stream items are replaced with duplicate items as shown and described above for the single stream in embodiment seven.

Eighth Embodiment—Structure

Referring to FIG. 9, the eight embodiment is applicable to embodiment one of this invention as an additional chemical second subsystem between lines 7 and 23. Duplicate components of items 8 through 22 (designated as 8 a through 22 a) are attached at tee junctions 7 and 23 respectively.

Similar chemical injection subsystem components in embodiments two through five can be employed as an additional second subsystem and attached to tee junctions 7 and 23 in their respective FIGS. 2 through 5.

Eighth Embodiment—Operations

The operations of the eighth embodiment is the same as in the embodiments one through five except when isolating one or both of the two subsystems. In general only one of the subsystems would be in operation at a time, although both could be in use at the same time. Two subsystems would allow for continuous chemical injection during refilling operations of the other. Two subsystems would also allow for significantly different injection rates by varying the capillary size (internal diameter and length) on the optional second subsystem.

CITATION LIST Patent Literature

U.S. Pat. No. 8,054,933 (Tran et al)

U.S. Pat. No. 2,266,981 (Miller)

U.S. Pat. No. 6,779,548 (McKeary)

Non Patent Literature

S. Hettiarachchi and T. P. Diaz, The On-Line NobleChem™ Application Experience In An Operating BWR, International Conference on Water Chemistry of Nuclear Reactor Systems, Jeju Island, South Korea, Oct. 23-26, 2006

S. E. Garcia, J. F. Giannelli and M. L. Jarvis, “BWR Chemistry Control Status: A Summary of Industry Chemistry Status Relative to the BWR Water Chemistry Guidelines”, Nuclear Plant Chemistry Conference 2010”, Quebec City, Canada, October 2010

P. L. Andresen and Y. J. Kim, “Developments in SCC Mitigation by Electrocatalysis,” 15th International Conference on Environmental Degradation of Materials in Nuclear Power Systems-—Water Reactors, Colorado Springs, Colo., Aug. 7-11, 2011 

We claim:
 1. A continuous passive chemical injection system for dispensing chemicals at a slow, controlled rate into a flowing process stream comprising: a. a bypass stream fluidly coupled to a process stream and taking fluid downstream of said process stream pump and returning the fluid further downstream into the process stream at a location where the fluid pressure in the process stream is lower than the inlet location. Said bypass stream consists of a heat exchange component (if required to reduce process stream temperatures to ambient), inlet temperature and pressure gauges (if required), a capillary pressure control valve, a differential conductivity meter, a bypass stream control valve, a bypass stream flow element with a differential pressure gauge and isolation valves at the bypass system flow entrance and flow exit locations. b. a chemical injection branch fluidly coupled to the bypass stream and consisting of a pressure vessel containing a bellows separator, a capillary solution flow control tube length with a differential pressure gauge, chemical solution fill and drain vent lines for the bellows and the pressure vessel plus isolation valves positioned at the beginning and end of the chemical injection branch. Said pressure vessel in the chemical injection branch is pressurized by a fluid connection originating at the inlet location of the bypass stream loop immediately downstream of the bypass stream loop inlet isolation valve which then enters the pressure vessel containing the bellows separator. Said bellows separator in the pressure vessel of the chemical injection branch is sealed between the two pressure vessel flanges or integral to one pressure vessel flange. Said pressurized bellows separator, filled with the chemical solution to be added to the process stream, due to the pressure in the pressure vessel, forces the chemical solution it contains through a capillary tube of sufficient diameter and length to result in the correct flow rate of chemical to be added to the bypass stream which in turn is added to the process stream. c. The rate of chemical injection is set by adjusting the capillary pressure control valve to establish the differential pressure across the capillary solution control tube to the desired pressure that results in the desired flow rate of chemical through the calibrated capillary solution control tube. The calibrated flow rate vs. differential pressure behavior of the capillary solution control tube is established before installation.
 2. The apparatus according to claim 1 wherein the pressure vessel in the chemical injection branch contains instead of a bellows separator contains a floating piston separator sealed against the sides of the pressure vessel in which one volume of the pressure vessel is pressurized by a fluid connection originating at the inlet location of the bypass stream loop immediately downstream of the bypass stream loop inlet isolation valve and other volume of the pressure vessel contain the chemical solution to be added to the process stream and fluidly connected with the inlet to the capillary tubing flow control device.
 3. The apparatus according to claim 1 wherein the pressure vessel in the chemical injection branch contains instead of a bellows separator contains a flexible membrane sealed between the pressure vessel flanges in which one volume of the pressure vessel is pressurized by a fluid connection originating at the inlet location of the bypass stream loop immediately downstream of the bypass stream loop inlet isolation valve and other volume of the pressure vessel contain the chemical solution to be added to the process stream and fluidly connected with the inlet to the capillary tubing flow control device.
 4. The apparatus according to claims 1, 2 and 3 wherein the capillary solution flow control tube length with a differential pressure gauge is upstream of the pressure vessel and is fluidly coupled to the bypass loop at a connection originating at the inlet location of the bypass stream loop immediately downstream of the bypass stream loop inlet isolation valve.
 5. The apparatus according to claims 1, 2 and 3 wherein the pressure in the volume of the pressure vessel used for pressurizing the vessel is established by a high pressure gas source coupled to a gas pressure regulator, instead of the liquid fluid connection to the inlet portion of the bypass loop.
 6. The apparatus according to claims 1 through 5 of wherein the line containing fluid in the bypass loop containing the chemical solution added via the chemical injection branch is teed into two process lines each containing similar bypass flow control valves, bypass flow orifices, bypass flow orifice differential pressure gauges, and are injected into two similar process streams.
 7. The apparatus according to claims 1 through 5 wherein the bypass flow control valve is removed, the flow metering orifice is replaced with a flow controlling orifice and the differential pressure gauge is replaced with a standard pressure gauge.
 8. The apparatus according to claims 1 through 5 wherein one or more additional pressure vessels and their separator devices are duplicated via the use of tee junctions at both the inlet and outlet lines such that only one vessel need be valved into the chemical addition branch at one time if necessary.
 9. The apparatus according to claims 1 through 8 where the use of a calibrated capillary tube is employed to control the flow rate of the chemical solution to be added to a process stream via adjusting the measured pressure drop across said capillary tube.
 10. The apparatus according to claims 1 through 9 wherein the length and the inner diameter of the capillary tube is chosen to provide the required range of desired flow rates over a selected range of differential pressure drop measured across said capillary tube.
 11. The apparatus according to claims 1 through 10 wherein the chemical supply vessel refill period can be adjusted by varying the supply vessel(s) volume, percentage of chemical concentration and solution injection flow rate to provide a continuous injection of a chemical solution over very long periods of up to and beyond two years without the necessity of refilling the chemical supply portion of the pressure vessel.
 12. Any version of the apparatus according to claims 1 through 5 and employing any of the variations according to claims 6 through 11 is capable of employing a solution of between 0.1 and 5.0% Na₂Pt(OH)₆ in the chemical solution portion of the pressure vessel to establish a constant, fixed Pt concentration in the final feedwater of a boiling water nuclear reactor of between 1 and 500 parts per trillion by weight over periods of time ranging from months to over two years.
 13. Any version of the apparatus according to claims 1 through 5 and employing any of the variations according to claims 6 through 11 is capable of employing a solution of any water soluble Pt based chemical in the solution portion of the pressure vessel to establish a constant, fixed Pt concentration in the final feedwater of a boiling water nuclear reactor of between 1 and 500 parts per trillion by weight over periods of time ranging from months to over two years.
 14. Any version of the apparatus according to claims 1 through 5 and employing any of the variations according to claims 6 through 11 is capable of employing a solution of any water soluble chemical to establish a target value of said chemical in a flowing liquid or gas process stream wherein that target value is a very dilute concentration in the range of parts per million, parts per billion or parts per trillion.
 15. The injection of the chemical solution is conducted without the utilization of pumps or other active components. The driving force for both the bypass side stream and chemical injection into said bypass stream is derived from the process stream pressure differential or by a regulated high pressure gas source. The only moving part is the floating separator within the chemical supply vessel. The bellows and flexible membrane freely move and do not make contact with vessel walls. The piston separator O-Rings do make contact with the vessel walls with 2 to 4 full strokes per year, thereby minimizing wear and tear for this motion.
 16. The low dilution concentration coupled with high bypass flow rate operating characteristics of this invention, reduces the probability of destructive thermal degradation of thermally sensitive chemical compounds flowing into high temperature, high pressure process streams.
 17. The multiple vessel apparatus in claim 8 can be used to seamlessly inject chemical solution without disruption on a continuous basis. This multiple vessel configuration can also be used to change chemical concentration in the bypass flow, thus the process stream, by having different concentrations of chemical in separate vessels or using different capillary tube dimensions. 